Communication control method and user terminal

ABSTRACT

A communication control method for performing an offload from a cellular RAN to a wireless LAN, includes a step of performing, by a user terminal, a network selection operation to select an appropriate access network with which a traffic of the user terminal is exchanged, from the cellular RAN and the wireless LAN on the basis of determination parameters. The determination parameters comprises at least one of: a cellular network status that is a network status concerning the cellular RAN; a wireless LAN network status that is a network status concerning the wireless LAN; a cellular radio link status that is a radio link status between the cellular RAN and the user terminal; and a wireless LAN radio link status that is a radio link status between the wireless LAN and the user terminal.

CROSS REFERENCE

The entire contents of U.S. Provisional Application No. 61/754,106(filed on Jan. 18, 2013), U.S. Provisional Application No. 61/808,777(filed on Apr. 5, 2013), U.S. Provisional Application No. 61/864,206(filed on Aug. 9, 2013), U.S. Provisional Application No. 61/864,219(filed on Aug. 9, 2013), and U.S. Provisional Application No. 61/898,791(filed on Nov. 1, 2013) are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a communication control method and auser terminal for working a cellular communication system in cooperationwith a wireless LAN system.

RELATED ART

In recent years, a user terminal (so-called dual terminal) that includesa cellular communication unit and a wireless LAN communication unit isbecoming widely used. Furthermore, a wireless LAN access point(hereinafter simply referred to as an “access point”) managed by anoperator of a cellular communication system increases.

Therefore, 3GPP (3rd Generation Partnership Project) which is a projectaiming to standardize a cellular communication system plans to considera technology capable of strengthening cooperation between a cellularcommunication system and a wireless LAN system (see Non-patent document1).

PRIOR ART DOCUMENT

[Non-Patent Document]

[Non-patent document 1] 3GPP contribution RP-1201455

SUMMARY OF THE INVENTION

It is considered that, when the cooperation between a cellularcommunication system and a wireless LAN system is strengthened, it ispossible to disperse a traffic load of the cellular base station to thewireless LAN system.

Therefore, it is an object of the present invention to provide acommunication control method and a user terminal capable of enhancingthe interworking between a cellular communication system and a wirelessLAN system.

A communication control method according to a first aspect is a methodfor performing an offload from a cellular RAN to a wireless LAN. Thecommunication control method includes a step of performing, by a userterminal, a network selection operation to select an appropriate accessnetwork with which a traffic of the user terminal is exchanged, from thecellular RAN and the wireless LAN on the basis of determinationparameters. The determination parameters comprises at least one of: acellular network status that is a network status concerning the cellularRAN; a wireless LAN network status that is a network status concerningthe wireless LAN; a cellular radio link status that is a radio linkstatus between the cellular RAN and the user terminal; and a wirelessLAN radio link status that is a radio link status between the wirelessLAN and the user terminal.

A user terminal according to a second aspect enables an offload from acellular RAN to a wireless LAN. The user terminal includes a controllerthat performs a network selection operation to select an appropriateaccess network with which a traffic of the user terminal is exchanged,from the cellular RAN and the wireless LAN on the basis of determinationparameters. The determination parameters comprises at least one of: acellular network status that is a network status concerning the cellularRAN; a wireless LAN network status that is a network status concerningthe wireless LAN; a cellular radio link status that is a radio linkstatus between the cellular RAN and the user terminal; and a wirelessLAN radio link status that is a radio link status between the wirelessLAN and the user terminal.

A communication control method according to a third aspect is a methodfor controlling a network selection operation that is an operation ofselecting, from a cellular RAN and a wireless LAN, an access networkwith which a traffic of a user terminal is exchanged. The communicationcontrol method includes: a step A of transmitting a common networkselection indicator for configuring one of ON and OFF of the networkselection operation, by the cellular RAN in a broadcast manner; and astep B of transmitting a dedicated network selection indicator forconfiguring one of ON and OFF of the network selection operation, by thecellular RAN in a unicast manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram according to a first embodimentand a second embodiment.

FIG. 2 is a block diagram of UE (user terminal) according to the firstembodiment and the second embodiment.

FIG. 3 is a block diagram of eNB (cellular base station) according tothe first embodiment and the second embodiment.

FIG. 4 is a block diagram of AP (access point) according to the firstembodiment and the second embodiment.

FIG. 5 is a protocol stack diagram of a radio interface in an LTEsystem.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem.

FIG. 7 is a diagram for illustrating an operation environment accordingto the first embodiment.

FIG. 8 is a sequence diagram of an operation pattern 1 according to thefirst embodiment.

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment.

FIG. 10 is a sequence diagram of an operation pattern 3 according to thefirst embodiment.

FIG. 11 is a sequence diagram of an operation pattern 4 according to thefirst embodiment.

FIG. 12 is a sequence diagram of an operation pattern 5 according to thefirst embodiment.

FIG. 13 is a sequence diagram of an operation pattern 6 according to thefirst embodiment.

FIG. 14 is a diagram for illustrating a specific example 1 of radio linkstability according to the first embodiment.

FIG. 15 is a diagram for illustrating a specific example 2 of radio linkstability according to the first embodiment.

FIG. 16 is a configuration diagram of a mapping table according to thefirst embodiment.

FIG. 17 is a diagram for illustrating an example of a determinationalgorithm according to the first embodiment.

FIG. 18 is a diagram illustrating a network selection control methodaccording to the second embodiment.

FIG. 19 is a sequence diagram of an operation pattern 1 according to thesecond embodiment.

FIG. 20 is a sequence diagram of an operation pattern 2 according to thesecond embodiment.

FIG. 21 is a sequence diagram of an operation pattern 3 according to thesecond embodiment.

FIG. 22 is a diagram for illustrating an operation according to otherembodiments.

FIG. 23 is a diagram for illustrating an operation according to otherembodiments.

DESCRIPTION OF EMBODIMENTS

[Overview of Embodiment]

A communication control method according to a first embodiment is amethod for performing an offload from a cellular RAN to a wireless LAN.The communication control method includes a step of performing, by auser terminal, a network selection operation to select an appropriateaccess network with which a traffic of the user terminal is exchanged,from the cellular RAN and the wireless LAN on the basis of determinationparameters. The determination parameters comprises at least one of: acellular network status that is a network status concerning the cellularRAN; a wireless LAN network status that is a network status concerningthe wireless LAN; a cellular radio link status that is a radio linkstatus between the cellular RAN and the user terminal; and a wirelessLAN radio link status that is a radio link status between the wirelessLAN and the user terminal.

In the first embodiment, the determination parameters further comprisesat least one of: a movement status of the user terminal; a batterystatus of the user terminal; and a power consumption status of the userterminal.

In the first embodiment, the step of performing the network selectionoperation comprises a step of measuring the wireless LAN radio linkstatus, by the user terminal.

In the first embodiment, the communication control method furtherincludes a step of transmitting, by the cellular RAN, information onnetwork selection. In the step of performing the network selectionoperation, the user terminal performs the network selection operation onthe basis of the information received from the cellular RAN.

In the first embodiment, the information comprises a network selectionindicator that indicates a need for the offload.

In the first embodiment, the information comprises a threshold to becompared with the determination parameters.

In the first embodiment, the information comprises identifiers of accesspoints provided in a coverage area of the cellular RAN. In the step ofmeasuring, the user terminal measures the wireless LAN radio link statuson the basis of the identifiers included in the information.

In the first embodiment, the wireless LAN radio link status comprises astability of radio link.

In the first embodiment, the communication control method furtherincludes a step of reporting, by the user terminal, the wireless LANradio link status to the cellular RAN.

In the first embodiment, the information comprises at least one of thecellular network status and the wireless LAN network status. In the stepof performing the network selection operation, the user terminalperforms the network selection operation on the basis of at least one ofthe cellular network status and the wireless LAN network status, as wellas the wireless LAN radio link status.

In the first embodiment, the information comprises information forcontrolling an operation of the user terminal that has discovered anaccess point that does not managed by an operator.

A user terminal according to the first embodiment enables an offloadfrom a cellular RAN to a wireless LAN. The user terminal includes acontroller that performs a network selection operation to select anappropriate access network with which a traffic of the user terminal isexchanged, from the cellular RAN and the wireless LAN on the basis ofdetermination parameters. The determination parameters comprises atleast one of: a cellular network status that is a network statusconcerning the cellular RAN; a wireless LAN network status that is anetwork status concerning the wireless LAN; a cellular radio link statusthat is a radio link status between the cellular RAN and the userterminal; and a wireless LAN radio link status that is a radio linkstatus between the wireless LAN and the user terminal.

A communication control method according to a second embodiment is amethod for controlling a network selection operation that is anoperation of selecting, from a cellular RAN and a wireless LAN, anaccess network with which a traffic of a user terminal is exchanged. Thecommunication control method includes: a step A of transmitting a commonnetwork selection indicator for configuring one of ON and OFF of thenetwork selection operation, by the cellular RAN in a broadcast manner;and a step B of transmitting a dedicated network selection indicator forconfiguring one of ON and OFF of the network selection operation, by thecellular RAN in a unicast manner.

In the second embodiment, the common network selection indicator isapplied to a user terminal in an idle state and a user terminal in aconnected state. The dedicated network selection indicator is appliedonly to a user terminal in a connected state.

In the second embodiment, the common network selection indicator isapplied only to a user terminal in an idle state. The dedicated networkselection indicator is applied only to a user terminal in a connectedstate.

In the second embodiment, in the step B, the cellular RAN transmits thededicated network selection indicator for configuring, to ON, thenetwork selection operation of a user terminal in a connected state. Theuser terminal in the connected state comprises a timer. The networkselection control method further comprises the steps of: starting thetimer when the network selection operation is configured to ON or whenthe user terminal in the connected state, in which the network selectionoperation is configured to ON, transitions to an idle state;maintaining, by the user terminal that has transitioned from theconnected state to the idle state, an ON configuration of the networkselection operation until the timer is expired; and clearing the ONconfiguration when the timer is expired.

In the second embodiment, in the step B, the cellular RAN transmits thededicated network selection indicator for configuring, to OFF, thenetwork selection operation of a user terminal in a connected state. Theuser terminal in a connected state comprises a timer. The networkselection control method further comprises the steps of: starting thetimer when the network selection operation is configured to OFF or whenthe user terminal in the connected state, in which the network selectionoperation is configured to OFF, transitions to an idle state;maintaining, by the user terminal that has transitioned from theconnected state to the idle state, an OFF configuration of the networkselection operation until the timer is expired; and clearing the OFFconfiguration when the timer is expired.

In the second embodiment, in the step B, a first cell included in thecellular RAN transmits the dedicated network selection indicator to afirst user terminal that connects to the first cell. The networkselection control method further comprises a step of transferringcontext information of the first user terminal from the first cell to asecond cell when the first user terminal performs handover to the secondcell from the first cell. The context information includes the dedicatednetwork selection indicator that has transmitted from the first cell tothe first user terminal.

In the second embodiment, the communication control method comprises thesteps of: determining, by the second cell that has received the contextinformation, whether to need a change of configuration indicated by thededicated network selection indicator included in the received contextinformation, on the basis of a load status of the second cell; andtransmitting a changed dedicated network selection indicator from thesecond cell to the first user terminal when it is determined that thechange of configuration is needed.

In the second embodiment, when a first user terminal that connects tothe first cell transitions to an idle state, a first cell included inthe cellular RAN transmits, to the first user terminal, a connectionrelease request including the dedicated network selection indicator.

[First Embodiment]

Below, with reference to the drawing, each embodiment will be describedin a case where an LTE system that is a cellular communication systemconfigured in compliance with the 3GPP standards is worked incooperation with a wireless LAN (WLAN) system.

(System Structure)

FIG. 1 is a system structure diagram according to the presentembodiment. As shown in FIG. 1, the LTE system includes a plurality ofUEs (User Equipments) 100, E-UTRAN (Evolved-UMTS Terrestrial RadioAccess Network) 10, and EPC (Evolved Packet Core) 20. The E-UTRAN 10corresponds to a radio access network. The EPC 20 corresponds to a corenetwork.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell with which a connection is established. The UE100 corresponds to the user terminal. The UE 100 is a terminal (dualterminal) that supports both communication schemes of cellularcommunication and WLAN communication.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). TheeNB 200 corresponds to a base station. The eNB 200 manages one or aplurality of cells and performs radio communication with the UE 100which establishes a connection with the cell of the eNB 200. It is notedthat the “cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a function ofperforming radio communication with the UE 100. Further, the eNB 200,for example, has a radio resource management (RRM) function, a routingfunction of user data, and a measurement control function for mobilitycontrol and scheduling.

The eNBs 200 are connected mutually via an X2 interface. Further, theeNB 200 is connected to MME/S-GW 500 included in the EPC 20 via an S1interface.

The EPC 20 includes a plurality of MME (Mobility ManagementEntity)/S-GWs (Serving-Gateways) 500. The MME is a network node thatperforms various mobility controls and the like, for the UE 100 andcorresponds to a controller. The S-GW is a network node that performstransfer control of user data and corresponds to a mobile switchingcenter.

The WLAN system (WLAN 30) includes WLAN AP (hereinafter referred to as“AP”) 300. The WLAN system is configured to be in compliance withvarious IEEE 802.11 specifications, for example. The AP 300 communicateswith the UE 100 in a frequency band (WLAN frequency band) different froma cellular frequency band. The AP 300 is connected to the EPC 20 via arouter, etc. However, the present invention is not limited to the casein which the eNB 200 and the AP 300 are individually collocated. The eNB200 and the AP 300 may also be collocated at the same place.Alternatively, the eNB 200 and the AP 300 may be directly connected toeach other through an arbitrary interface of an operator.

Subsequently, a structure of the UE 100, the eNB 200, and the AP 300will be described.

FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100includes: antennas 101 and 102; a cellular transceiver (cellularcommunication unit) 111; a WLAN transceiver (WLAN communication unit)112; a user interface 120; a GNSS (Global Navigation Satellite System)receiver 130; a battery 140; a memory 150; and a processor 160. Thememory 150 and the processor 160 constitute a control unit. The UE 100may not have the GNSS receiver 130. Furthermore, the memory 150 may beintegrally formed with the processor 160, and this set (that is, achipset) may be called a processor 160′.

The antenna 101 and the cellular transceiver 111 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 111 converts a baseband signal output from the processor 160into the cellular radio signal, and transmits the same from the antenna101. Further, the cellular transceiver 111 converts the cellular radiosignal received by the antenna 101 into the baseband signal, and outputsthe same to the processor 160.

The antenna 102 and the WLAN transceiver 112 are used for transmittingand receiving a WLAN radio signal. The WLAN transceiver 112 converts thebaseband signal output from the processor 160 into a WLAN radio signal,and transmits the same from the antenna 102. Further, the WLANtransceiver 112 converts the WLAN radio signal received by the antenna102 into a baseband signal, and outputs the same to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, andvarious buttons. Upon receipt of the input from a user, the userinterface 120 outputs a signal indicating a content of the input to theprocessor 160. The GNSS receiver 130 receives a GNSS signal in order toobtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor 160. The battery140 accumulates a power to be supplied to each block of the UE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 150. The processor 160 may further include a codecthat performs encoding and decoding on sound and video signals. Theprocessor 160 executes various processes and various communicationprotocols described later.

FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB200 includes an antenna 201, a cellular transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 constitute a control unit.

The antenna 201 and the cellular transceiver 210 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 210 converts the baseband signal output from the processor240 into the cellular radio signal, and transmits the same from theantenna 201. Furthermore, the cellular transceiver 210 converts thecellular radio signal received by the antenna 201 into the basebandsignal, and outputs the same to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 via anX2 interface and is connected to the MME/S-GW 500 via the S1 interface.Further, the network interface 220 is used for communication with the AP300 via the EPC 20.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 implements various processesand various communication protocols described later. Furthermore, thememory 230 may be integrally formed with the processor 240, and this set(that is, a chipset) may be called a processor 240′.

FIG. 4 is a block diagram of the AP 300. As shown in FIG. 4, the AP 300includes an antenna 301, a WLAN transceiver 311, a network interface320, a memory 330, and a processor 340.

The antenna 301 and the WLAN transceiver 311 are used for transmittingand receiving the WLAN radio signal. The WLAN transceiver 311 convertsthe baseband signal output from the processor 340 into the WLAN radiosignal and transmits the same from the antenna 301. Further, the WLANtransceiver 311 converts the WLAN radio signal received by the antenna301 into the baseband signal and outputs the same to the processor 340.

The network interface 320 is connected to the EPC 20 via a router, etc.Further, the network interface 320 is used for communication with theeNB 200 via the EPC 20.

The memory 330 stores a program to be executed by the processor 340 andinformation to be used for a process by the processor 340. The processor340 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 330.

FIG. 5 is a protocol stack diagram of a radio interface in the LTEsystem. As illustrated in FIG. 5, the radio interface protocol isclassified into a layer 1 to a layer 3 of an OSI reference model,wherein the layer 1 is a physical (PHY) layer. The layer 2 includes aMAC (Media Access Control) layer, an RLC (Radio Link Control) layer, anda PDCP (Packet Data Convergence Protocol) layer. The layer 3 includes anRRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, data is transmitted via the physical channel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, data is transmitted via atransport channel. The MAC layer of the eNB 200 includes a schedulerthat selects a transport format (a transport block size, a modulationand coding scheme and the like) of an uplink and a downlink, and anassigned resource block.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control message (anRRC message) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When there is a connection (RRC connection) between theRRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in aconnected state (RRC connected state), otherwise, the UE 100 is in anidle state (RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management, mobility management and the like.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency DivisionMultiplexing Access) is applied to a downlink, and SC-FDMA (SingleCarrier Frequency Division Multiple Access) is applied to an uplink,respectively.

As illustrated in FIG. 6, the radio frame is configured by 10 subframesarranged in a time direction, wherein each subframe is configured by twoslots arranged in the time direction. Each subframe has a length of 1 msand each slot has a length of 0.5 ms. Each subframe includes a pluralityof resource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. The resource block includes a pluralityof subcarriers in the frequency direction. Among radio resourcesassigned to the UE 100, a frequency resource can be designated by aresource block and a time resource can be designated by a subframe (orslot).

(Operation According to First Embodiment)

Next, an operation according to the present embodiment will bedescribed.

FIG. 7 is a diagram for illustrating an operation environment accordingto the present embodiment. As illustrated in FIG. 7, a plurality of APs300 are provided in a coverage of the eNB 200. Each of the plurality ofAPs 300 is AP (Operator controlled AP) managed by an operator. FIG. 7illustrates only three APs 300; however, in an actual environment, alarge number of APs 300 are provided in the coverage of the eNB 200.

In the actual environment, APs (Non-operator controlled APs) notcontrolled by the operator also exist. The Non-operator controlled APsinclude public APs (so-called Free WiFi) opened free of charge, and APsowned by a user.

Furthermore, a plurality of UEs 100 are positioned in the coverage ofthe eNB 200. UE 100-1 to UE 100-3 are connected to the eNB 200, andperform cellular communication with the eNB 200. UE 100-4 is connectedto AP 300-3, and performs WLAN communication with the AP 300-3.

When the eNB 200 houses a large number of UEs 100, a load level of theeNB 200 increases. The “load level” herein indicates the degree ofcongestion of the eNB 200 such as a traffic load of the eNB 200 or radioresource use ratio of the eNB 200. Thus, at least a part of trafficexchanged between the UE 100 and the eNB 200 is allowed to transition tothe wireless LAN system, so that it is possible to disperse the load ofthe eNB 200 to the wireless LAN system.

Hereinafter, a description will be provided for an operation pattern sothat traffic exchanged between the UE 100 and the eNB 200 is allowed totransition (hereinafter referred to as “offload”) to the wireless LANsystem. The offload herein includes the case in which at least a part ofthe traffic is allowed to transition to the wireless LAN system whilemaintaining a connection with the eNB 200, as well as the case in whichall of the traffic exchanged between the UE 100 and the eNB 200 isallowed to transition to the wireless LAN system.

An operation pattern 1 is a pattern in which the eNB 200 selects AP 300to which an offload is destined (that is, a traffic transitiondestination). On the other hand, an operation pattern 2 is a pattern inwhich the UE 100 selects the AP 300 of the offload destination.

Furthermore, an operation pattern 3 is a mixed pattern of the operationpatterns 1 and 2, and is a pattern in which the eNB 200 finally selectsthe AP 300 of the offload destination. An operation pattern 4 is a mixedpattern of the operation patterns 1 and 2, and is a pattern in which theUE 100 finally selects the AP 300 of the offload destination. Anoperation pattern 5 is a mixed pattern of the operation patterns 3 and4.

An operation pattern 6 is a pattern in which the Non-operator controlledAP is considered.

In each of the operation patterns, it is assumed that the UE 100 is in astate in which the UE 100 is connected to the eNB 200 (connected state),and the WLAN transceiver 112 of the UE 100 is in an operation state (ONstate). In an initial state, the UE 100 may be in an idle state. In thiscase, the UE 100 establishes a connection with the eNB 200 if needed.Furthermore, it is assumed that the eNB 200 can acquire information onthe Operator controlled AP in the coverage of the eNB 200 via abackhaul, for example.

(1) Operation Pattern 1

FIG. 8 is a sequence diagram of the operation pattern 1.

As illustrated in FIG. 8, in step S101, the eNB 200 transmits, to the UE100, WLAN measurement configuration information for controllingmeasurement for the wireless LAN system (wireless LAN measurement). TheeNB 200, for example, transmits the WLAN measurement configurationinformation to the UE 100 by employing handover of the UE 100, selectionof the UE 100, a paging area change of the UE 100, or a change of anetwork status as a trigger. Alternatively, the eNB 200 may transmit theWLAN measurement configuration information to the UE 100 by employing,as a trigger, the fact that the load level of the eNB 200 exceeds athreshold value.

The WLAN measurement configuration information includes each ofidentifiers of a plurality of APs 300 (Operator controlled APs) providedin the coverage area of the eNB 200. The identifier (hereinafterreferred to as an “AP identifier”) of the AP 300 indicates SSID (ServiceSet Identifier), BSSID (Basic Service Set Identifier), or an arbitraryID that identifies AP designed by an operator.

The WLAN measurement configuration information may also includeinformation indicating how a radio link status between the UE 100 andthe AP 300 should be measured, and information indicating how ameasurement result (for example, a report trigger) should be reported.Moreover, the WLAN measurement configuration information may alsoinclude information indicating which operation patterns (the operationpatterns 1 to 5) to be followed.

The WLAN measurement configuration information may also includeinformation indicating whether or not to confirm a measurementconfiguration (whether or not to perform wireless LAN measurement) evenwhen the UE 100 is connected to the AP 300. Furthermore, it ispreferable that the UE 100 continues to confirm the measurementconfiguration until an optimal AP 300 is selected. On the other hand,after the UE 100 starts offload to the AP 300, it is preferable not toconfirm the measurement configuration in order to reduce a processingload.

In step S102, the UE 100 detects APs 300 on the basis of the APidentifiers included in the WLAN measurement configuration information.Since each AP 300 transmits a beacon signal including the AP identifierof the AP 300, the UE 100 scans the beacon signal including the APidentifiers included in the WLAN measurement configuration information,thereby the UE 100 can detect the APs 300.

In step S103, the UE 100 performs wireless LAN measurement according tothe WLAN measurement configuration information. The UE 100 measures aradio link status between the detected AP 300 and the UE 100. The radiolink status includes signal strength of the beacon signal, radio linkstability (details thereof will be described later) and the like.Furthermore, when the beacon signal includes information indicating aload level of the AP 300 (that is, load information), the UE 100 mayacquire the load information.

In step S104, the UE 100 reports the measured radio link status to theeNB 200. Specifically, the UE 100 associates the AP identifiers with theradio link status (the signal strength of the beacon signal, the radiolink stability and the like), and transmits a WLAN measurement reportincluding the radio link status and the AP identifiers to the eNB 200.Moreover, the UE 100 may control the WLAN measurement report to includethe load information of the AP 300. Furthermore, the UE 100 may alsocontrol the WLAN measurement report to include information on a movementspeed, a battery level and the like of the UE 100.

In step S105, the eNB 200 having received the WLAN measurement reportfrom the UE 100 determines whether or not to offload traffic of the UE100. For example, the eNB 200, when the load level of the eNB 200exceeds a threshold value, determines to offload the traffic of the UE100. Alternatively, when communication quality between the UE 100 andthe eNB 200 deteriorates or when the movement speed of the UE 100 issufficiently slow and the battery level of the UE 100 is sufficient, theeNB 200 may determine to offload the traffic of the UE 100. Hereinafter,the following description will be given on the assumption that the eNB200 has determined to offload the traffic of the UE 100.

In step S106, the eNB 200 determines whether to select AP 300 of anoptimal offload destination or maintain communication with the eNB 200on the basis of the radio link status based on the WLAN measurementreport, and a network status concerning the eNB 200 and/or AP 300(hereinafter simply referred to as a “network status”). The networkstatus indicates a load level (that is, degree of congestion) of the AP300 (or the eNB 200). Alternatively, the network status may indicatecommunication capability of the AP 300 (or the eNB 200). Thecommunication capability includes whether QoS guarantee (WMM) ispossible or not possible. Furthermore, a specific example of adetermination algorithm for prioritizing APs 300 will be describedlater.

In step S107, the eNB 200 transmits, to the UE 100, an offloading oderto the selected AP 300. The offloading order includes AP identifier ofthe AP 300 selected by the eNB 200. The offloading order may includeinformation indicating the type of traffic (a bearer) to be offloaded.

In step S108, the UE 100 starts offload to the AP 300 selected by theeNB 200 according to the offloading order from the eNB 200. Furthermore,when the UE 100 is not connected yet to the AP 300 selected by the eNB200, the UE 100 starts offload after connecting to the AP 300.

The WLAN measurement report transmitted from the UE 100 in step S104 mayinclude location information on the UE 100.

(2) Operation Pattern 2

FIG. 9 is a sequence diagram of the operation pattern 2. Hereinafter, adescription overlapping that of the operation pattern 1 will be omitted.

As illustrated in FIG. 9, in step S201, the eNB 200 transmits WLANmeasurement configuration information to the UE 100. In the operationpattern 2, the eNB 200 controls the WLAN measurement configurationinformation to include a network status and transmits the WLANmeasurement configuration information to the UE 100. In this way, thenetwork status is notified to the UE 100.

In step S202, the UE 100 detects APs 300 on the basis of AP identifiersincluded in the WLAN measurement configuration information.

In step S203, the UE 100 performs wireless LAN measurement according tothe WLAN measurement configuration information. Then, the UE 100determines whether to select AP 300 of an optimal offload destination ormaintain communication with the eNB 200 on the basis of a radio linkstatus between the UE 100 and detected APs 300 and a network statusnotified from the eNB 200.

In step S204, the UE 100 further includes a step of notifying the eNB200 of information on the selected AP 300. The information on theselected AP 300 may indicate AP identifier of the AP 300.

In step S205, the eNB 200 determines whether or not to offload trafficof the UE 100. Hereinafter, the following description will be given onthe assumption that the eNB 200 has determined to offload the traffic ofthe UE 100.

In step S206, the eNB 200 notifies the UE 100 of offload authorization”to the AP 300 selected by the UE 100.

In step S207, the UE 100 starts offload to the selected AP 300 inresponse to the offload authorization from the eNB 200.

Furthermore, in the present sequence, the process of step S205 may notnecessarily be performed. The processes of steps S204 to S206 may notnecessarily be performed.

(3) Operation Pattern 3

FIG. 10 is a sequence diagram of the operation pattern 3. Hereinafter, adescription overlapping that of the operation patterns 1 and 2 will beomitted.

As illustrated in FIG. 10, in step S301, the eNB 200 transmits WLANmeasurement configuration information to the UE 100.

In step S302, the UE 100 detects APs 300 on the basis of AP identifiersincluded in the WLAN measurement configuration information.

In step S303, the UE 100 performs wireless LAN measurement according tothe WLAN measurement configuration information. Then, on the basis of aradio link status between the UE 100 and the detected APs 300, the UE100 calculates priority in which each of the detected APs 300 isemployed as a transition destination of traffic. Furthermore, the UE 100considers whether to advance offload in consideration of a movementspeed or a battery level of the UE 100, and also prioritizes a cellularnetwork (the eNB 200).

In step S304, the UE 100 transmits priority information on thecalculated priority to the eNB 200. Specifically, the UE 100 transmits,to the eNB 200, a list (hereinafter referred to as a “priority list”) inwhich AP identifiers are arranged according to the calculated priority.

In step S305, the eNB 200 determines whether or not to offload trafficof the UE 100. Hereinafter, the following description will be given onthe assumption that the eNB 200 has determined to offload the traffic ofthe UE 100.

In step S306, on the basis of the priority list and a network status,the eNB 200 determines whether to select AP 300 of an optimal offloaddestination or maintain communication with the eNB 200.

In step S307, the eNB 200 transmits, to the UE 100, an offloading orderto the selected AP 300.

In step S308, the UE 100 starts offload to the AP 300 selected by theeNB 200 according to the offloading order from the eNB 200.

(4) Operation Pattern 4

FIG. 11 is a sequence diagram of the operation pattern 4. Hereinafter, adescription overlapping that of the operation patterns 1 to 3 will beomitted.

As illustrated in FIG. 11, in step S401, the eNB 200 transmits WLANmeasurement configuration information to the UE 100.

In step S402, the UE 100 detects APs 300 on the basis of AP identifiersincluded in the WLAN measurement configuration information.

In step S403, the UE 100 performs wireless LAN measurement according tothe WLAN measurement configuration information. Then, the UE 100associates the AP identifiers with a measured radio link status (signalstrength of a beacon signal, radio link stability and the like), andtransmits a WLAN measurement report including the radio link status andthe AP identifiers to the eNB 200. Furthermore, the UE 100 may controlthe WLAN measurement report to include information on a movement speed,a battery level and the like of the UE 100.

In step S404, the eNB 200 determines whether or not to offload trafficof the UE 100. Hereinafter, the following description will be given onthe assumption that the eNB 200 has determined to offload the traffic ofthe UE 100.

In step S405, on the basis of the radio link status based on the WLANmeasurement report, and a network status, the eNB 200 calculatespriority in which each of the APs 300 (the AP identifiers) included inthe WLAN measurement report is employed as a transition destination oftraffic. The priority may also include the eNB 200. In addition, in stepS404 and/or step S403, the eNB 200 may take the movement speed, thebattery level and the like of the UE 100 into consideration.

In step S406, the eNB 200 transmits a priority list to the UE 100 on thebasis of the calculated priority.

In step S407, on the basis of the priority list and the radio linkstatus, the UE 100 selects AP 300 of an optimal offload destination.

In step S408, the UE 100 notifies the eNB 200 of the AP identifier ofthe selected AP 300.

In step S409, the UE 100 starts offload to the selected AP 300.

(5) Operation Pattern 5

FIG. 12 is a sequence diagram of the operation pattern 5. Hereinafter, adescription overlapping that of the operation patterns 1 to 4 will beomitted.

As illustrated in FIG. 12, in step S501, the eNB 200 transmits WLANmeasurement configuration information to the UE 100.

In step S502, the UE 100 detects APs 300 on the basis of AP identifiersincluded in the WLAN measurement configuration information.

In step S503, the UE 100 performs wireless LAN measurement according tothe WLAN measurement configuration information. The UE 100 measuressignal strength of a beacon signal of a radio link status. Then, on thebasis of the measured signal strength, the UE 100 calculates priority inwhich each of the detected APs 300 is employed as a transitiondestination of traffic.

In step S504, the UE 100 transmits a priority list to the eNB 200 on thebasis of the calculated priority.

In step S505, on the basis of the priority list from the UE 100 and anetwork status, the eNB 200 updates the priority list from the UE 100such that the network status is reflected.

In step S506, the UE 100 performs the wireless LAN measurement again.The UE 100 measures radio link stability of the radio link status.

In step S507, the eNB 200 transmits the updated priority list to the UE100.

In step S508, on the basis of the priority list from the eNB 200 and themeasured radio link stability, the UE 100 determines whether to selectAP 300 of an optimal offload destination or maintain communication withthe eNB 200. At this time, a battery level and the like of the UE 100may be considered.

In step S509, the UE 100 notifies the eNB 200 of the AP identifier ofthe selected AP 300.

In step S510, the eNB 200 determines whether or not to offload trafficof the UE 100. Hereinafter, the following description will be given onthe assumption that the eNB 200 has determined to offload the traffic ofthe UE 100.

In step S511, the eNB 200 notifies the UE 100 of offload authorizationto the AP 300 selected by the UE 100.

In step S512, the UE 100 starts offload to the selected AP 300 inresponse to the offload authorization from the eNB 200.

Furthermore, in the present sequence, the process of step S510 may notnecessarily be performed. Furthermore, in the present sequence, theprioritization is performed twice in total (steps S503 and S505);however, the prioritization may be performed three times or more.

(6) Operation Pattern 6

FIG. 13 is a sequence diagram of the operation pattern 6. Hereinafter, adescription overlapping that of the operation patterns 1 to 5 will beomitted.

As illustrated in FIG. 13, in step S601, the eNB 200 transmits WLANmeasurement configuration information to the UE 100. In the operationpattern 6, the WLAN measurement configuration information furtherincludes at least any one piece of information of the following 1) to 3)in order to control an operation of the UE 100 when the UE 100 discoversAP (Non-operator controlled AP) not controlled by an operator.

1) Information indicating whether the UE 100 leaves traffic in cellularcommunication when the UE 100 is connected to the Non-operatorcontrolled AP (for example, whether to leave voice data such as atelephone or data other than E-mail). For example, when a load level ofthe eNB 200 is high (congested), it is preferable not to leave trafficin the cellular communication.

2) Information indicating whether or not to notify the eNB 200 of the UE100 being connected to the Non-operator controlled AP.

3) Information indicating whether or not to continuously search (scan)an Operator controlled AP when the UE 100 is connected to theNon-operator controlled AP.

In step S602, the UE 100 detects APs 300 on the basis of AP identifiersincluded in the WLAN measurement configuration information.

In step S603, the UE 100 detects the Non-operator controlled AP andconnects to the Non-operator controlled AP.

In step S604, the UE 100 starts a connection to the AP 300 (the Operatorcontrolled AP) on the basis of the information of 3) described above.

In step S605, the UE 100 transmits, to the eNB 200, a notificationindicating that the UE 100 is connected to the Non-operator controlledAP. However, when the notification is rendered unnecessary by theinformation of 2) described above, the process of step S604 may not beperformed.

(7) Radio Link Stability

The radio link stability indicates the degree of stability of a radiolink between the UE 100 and the AP 300. Hereinafter, specific examples 1to 4 of the radio link stability will be described.

FIG. 14 is a diagram for illustrating the specific example 1 of theradio link stability. As illustrated in FIG. 14, in the specific example1, the UE 100 measures a time (Tover_thresh.) for which the signalstrength of a beacon signal exceeds a threshold value, and acquires, asthe radio link stability, a value of the longest Tover_thresh. in ameasurement interval or an average value of Tover_thresh. in themeasurement interval.

FIG. 15 is a diagram for illustrating the specific example 2 of theradio link stability. As illustrated in FIG. 15, in the specific example2, the UE 100 acquires variance of the signal strength of a beaconsignal in a measurement interval as the radio link stability.

In the specific example 3, the UE 100 acquires a ratio of desired wavesignals out of received signals as the radio link stability. Forexample, the UE 100 acquires (the reception strength of a beacon signalcorresponding to a desired BSSID)/(signal strength in the same frequencyband) as the radio link stability.

In the specific example 4, the UE 100 acquires, as the radio linkstability, the number of times by which signals from BSSID of the AP 300to be measured (all signals including a beacon signal) are received in ameasurement interval. For example, the UE 100 acquires, as the radiolink stability, (the number of times by which a signal corresponding toa desired BSSID is received)/the measurement interval. Since AP 300dealing with heavy traffic frequently transmits signals, it is possibleto regard a radio link as being stable when the number of receptions issmall.

Furthermore, in the specific examples 1 to 4, the UE 100 is able tomeasure the radio link stability for all APs 300, however, the UE 100may measure the signal strength of the beacon signal, then select AP 300with high signal strength, connect to the selected AP 300, and measurethe radio link stability only for the AP 300. For example, the UE 100may transmit a connection confirmation message to the connected AP 300,measure a passage rate, and measure the radio link stability. Then, whenthe measured radio link stability satisfies a condition, the UE 100 maytransmit a report to the eNB 200.

(8) WLAN Measurement Report

The WLAN measurement report, which is transmitted from the UE 100 to theeNB 200, includes the radio link status (the signal strength of thebeacon signal, the radio link stability and the like) and the APidentifiers. The radio link status is not indicated by an immediatevalue but is indicated by an index value in each fixed range, so that itis possible to reduce overhead.

FIG. 16 is a configuration diagram of a mapping table according to thepresent embodiment. The mapping table is shared between the eNB 200 andthe UE 100.

As illustrated in FIG. 16, the mapping table is a table in whichmeasured values of the radio link status are associated with indexvalues. The UE 100 converts the measured values to the index values withreference to the mapping table, and controls the WLAN measurement reportto include the index values.

(9) Determination Algorithm

An example of a determination algorithm for prioritizing APs 300 will bedescribed. FIG. 17 is a diagram for illustrating an example of thedetermination algorithm.

As illustrated in FIG. 17, the UE 100 or the eNB 200 performs weightingcalculation with respect to each index value of a determinationparameter (a radio link status, a network status and the like) for eachAP, thereby being able to determine an optimal AP. For example, the UE100 or the eNB 200 calculates an evaluation value for each AP by thefollowing calculation formula and sets priority to be high in descendingorder of the evaluation value.(Load level)*LoadWeight+(Signal strength level+Link stabilitylevel)*LinkWeight

[Modification of First Embodiment]

The UE 100 may transmit the WLAN measurement report to the eNB 200together with a cellular measurement report that is a report of ameasurement result for the eNB 200 and (a neighboring eNB).

In the above-described embodiments, the WLAN transceiver 112 of the UE100 is assumed to be in an operation state (an ON state); however, itmay be possible to employ an operation considering the case in which theWLAN transceiver 112 is in a stop state (an OFF state). For example, theUE 100 may transmit, to the eNB 200, information indicating whether ornot the WLAN transceiver 112 is in the operation state, and the eNB 200may transmit WLAN measurement configuration information only to the UE100 including the WLAN transceiver 112 in the operation state.

Alternatively, even when the UE 100 including the WLAN transceiver 112in the stop state receives the WLAN measurement configurationinformation from the eNB 200, the UE 100 may ignore the WLAN measurementconfiguration information. Furthermore, the UE 100 may hold the WLANmeasurement configuration information when ignoring the WLAN measurementconfiguration information, and start measurement with reference to theWLAN measurement configuration information when the WLAN transceiver 112transitions to the operation state.

In the above-described embodiments, as one example of the cellularcommunication system, the LTE system is described; however, the presentinvention is not limited to the LTE system, and the present inventionmay be applied to systems other than the LTE system.

When it is determined whether to perform offload to the WLAN 30 or tostay in the cellular network (the E-UTRAN 10), the determination may bemade in consideration not only of a power consumption status of the UE100 (brightness setting of a screen, a reduction speed of a batterylevel, and the like) but also of the battery level. The battery levelmay be determined by percentage, may be determined by using a thresholdvalue and the like, or may be weighted, be included into otherparameters and the like of radio field strength, and may be subject tocomprehensive evaluation.

[Second Embodiment]

The second embodiment will be described while focusing on thedifferences from the first embodiment. In the second embodiment, thecase, in which the UE 100 has a decision right of an access network in anetwork selection operation, will be mainly assumed.

[Overview of Second Embodiment]

A network selection control method according to the second embodiment isa method of controlling a network selection operation that is anoperation of selecting an access network that houses traffic of the UE100, from the cellular RAN (the E-UTRAN 10) and the WLAN 30.

FIG. 18 is a diagram illustrating a network selection control methodaccording to the second embodiment.

As illustrated in FIG. 18, the network selection control methodaccording to the second embodiment includes step S1101 (step A) oftransmitting a common network selection indicator for configuring ON orOFF of the network selection operation from the E-UTRAN 10 (the cellularRAN) in a broadcast manner, and step S1102 (step B) of transmitting adedicated network selection indicator for configuring ON or OFF of thenetwork selection operation from the E-UTRAN 10 in a unicast manner.

As described above, the network selection indicator (Access NetworkSelection Indicator) for configuring the ON or OFF of the networkselection operation is transmitted from the cellular RAN to the UE 100,so that it is possible to control ON or OFF of the network selectionoperation in the UE 100 without notifying the UE 100 of a load statusand the like of the cellular RAN.

In addition, the common network selection indicator may be included intoSIB (System Information Block). On the other hand, the dedicated networkselection indicator may be included into an RRC ConnectionReconfiguration message or an RRC Connection Release message. The RRCConnection Release message corresponds to a connection release request.

In the second embodiment, the common network selection indicator isapplied to UE 100 in an idle state and UE 100 in a connected state. Thededicated network selection indicator is applied only to the UE 100 in aconnected state.

Alternatively, the common network selection indicator is applied only tothe UE 100 in an idle state. The dedicated network selection indicatoris applied only to the UE 100 in a connected state.

(Operation Pattern 1)

FIG. 19 is a sequence diagram of an operation pattern 1 according to thesecond embodiment. In an initial state of the present sequence, asillustrated in step S1201, the UE 100 is in a state of havingestablished a connection with a cell (the eNB 200) included in theE-UTRAN 10. The UE 100 has a timer.

As illustrated in FIG. 19, in step S1202, the E-UTRAN 10 controls thededicated network selection indicator for configuring the networkselection operation to ON to be included into the RRC ConnectionReconfiguration message, and transmits the RRC ConnectionReconfiguration message to UE 100 in a connected state.

In step S1203, the UE 100 having received the dedicated networkselection indicator (the network selection operation: ON), configuresthe network selection operation to ON. In this way, the UE 100 startsthe selection of an appropriate access network that houses the trafficof the UE 100, from the E-UTRAN 10 and the WLAN 30.

In step S1204, the UE 100 transitions from the connected state to theidle state.

In step S1205, the UE 100 starts to operate the timer when the UE 100configures the network selection operation to ON (step S1203) ortransitions to the idle state (step S1204). The timer is used to specifya time for which the ON Configuration of the network selection operationshould be maintained.

The UE 100 having transitioned from the connected state to the idlestate, maintains the ON configuration of the network selection operationuntil the timer is expired.

In step S1206, the UE 100 abandons the ON configuration of the networkselection operation when the timer is expired.

As described above, in the operation pattern 1 according to the secondembodiment, even the UE 100 having transitioned to the idle state,operates according to the dedicated network selection indicator in thetime corresponding to the timer. Thus, even when the common networkselection indicator indicates OFF, it is possible to continue thenetwork selection operation according to the dedicated network selectionindicator indicating ON.

Furthermore, the operation pattern 1 according to the second embodimentdescribes the case in which the network selection operation isintentionally maintained to ON; however, the network selection operationmay be intentionally changed to be maintained to OFE In this case, inthe sequence of the operation pattern 1 according to the secondembodiment, “ON” is regarded as “OFF”. In this way, even in the case inwhich the common network selection indicator indicates ON, it ispossible to operate the UE 100 according to the dedicated networkselection indicator indicating OFF.

(Operation Pattern 2)

FIG. 20 is a sequence diagram of an operation pattern 2 according to thesecond embodiment. In an initial state of the present sequence, asillustrated in step S1301, the UE 100 is in a state of havingestablished a connection with a cell 1 (eNB 200-1) included in theE-UTRAN 10.

As illustrated in FIG. 20, in step S1302, the cell 1 (the eNB 200-1)included in the E-UTRAN 10 controls the dedicated network selectionindicator to be included into the RRC Connection Reconfigurationmessage, and transmits the RRC Connection Reconfiguration message to UE100 that connects to the cell 1.

In step S1303, the UE 100 having received the dedicated networkselection indicator, configures the network selection operation to ON orOFF according to the dedicated network selection indicator.

In step S1304, the UE 100 transmits a measurement report to the cell 1.The measurement report, for example, includes each of measurementresults of the serving cell (the cell 1) and a neighboring cell (a cell2) in the E-UTRAN 10.

In step S1305, the cell 1 (the eNB 200-1) having received themeasurement report, decides handover of the UE 100 to the cell 2 on thebasis of the received measurement report.

In step S1306, the cell 1 (the eNB 200-1) transmits a handover requestincluding context information of the UE 100 to the cell 2 (eNB 200-2).The context information is information on various configurations of theUE 100. The context information includes the dedicated network selectionindicator transmitted from the cell 1 to the UE 100 in step S1302.

As described above, the context information including the dedicatednetwork selection indicator is transferred from the cell 1 to the cell2. In this way, the cell 2 (the eNB 200-2) is able to recognize thenetwork selection configuration of the UE 100.

In step S1307, the cell 2 (the eNB 200-2) having received the handoverrequest, transmits a handover acknowledgment (ACK) to the cell 1 (theeNB 200-1).

In step S1308, the cell 1 (the eNB 200-1) having received the handoveracknowledgment, transmits, to the UE 100, a handover command thatinstructs handover to the cell 2.

In step S1309, the UE 100 having received the handover command, performsa connection process with the cell 2.

The cell 2 (the eNB 200-2) having received the context information,determines whether or not a change in the dedicated network selectionindicator (that is, the network selection configuration of the UE 100)included in the context information is necessary on the basis of theload status of the cell 2. For example, when OFF is configured in the UE100 and the load level of the cell 2 (the eNB 200-2) is high, it isdetermined to change the OFF configuration to the ON configuration.

When it is determined that such a change is necessary, the cell 2 (theeNB 200-2) transmits a changed dedicated network selection indicator(for example, the network selection operation: ON) to the UE 100. Inaddition, the cell 2 (the eNB 200-2) may transmit the changed dedicatednetwork selection indicator to the UE 100 when the UE 100 performs theconnection process in step S1309.

As described above, in the operation pattern 2 according to the secondembodiment, even when the UE 100 performs handover, a target cell (thecell 2) is able to recognize the network selection configuration of theUE 100. Thus, the target cell (the cell 2) performs determinationregarding whether or not to change the network selection configurationof the UE 100, and can change the network selection configurationaccording to necessity.

(Operation Pattern 3)

FIG. 21 is a sequence diagram of the operation pattern 3 according tothe second embodiment. In an initial state of the present sequence, asillustrated in step S1401, the UE 100 is in a state of havingestablished a connection with the cell (the eNB 200) included in theE-UTRAN 10.

As illustrated in FIG. 21, in step S1402, the cell included in theE-UTRAN 10 transmits the RRC Connection Release message including thededicated network selection indicator to the UE 100. The UE 100 havingreceived the RRC Connection Release message, configures the networkselection operation to ON or OFF according to the dedicated networkselection indicator included in the RRC Connection Release message.Then, in step S1403, the UE 100 releases an RRC connection andtransitions from a connected state to an idle state.

As described above, in the operation pattern 3 according to the secondembodiment, since the UE 100 configures the network selection operationto ON or OFF when transitioning to the idle state, it is possible tocontrol the UE 100 in the idle state to operate according to thededicated network selection indicator.

In addition, the UE 100 transitions to the idle state and then performsany one of the following operations.

1) The UE 100 maintains a configuration until the UE 100 reaches a nextconnected state and receives the dedicated network selection indicator.

2) Similarly to the above-described operation pattern 1 according to thesecond embodiment, the UE 100 maintains a configuration until the timeris expired, and operates according to the common network indicatorreceived after the timer is expired.

Hereinafter, additional statements for the above-described embodimentswill be described.

[Additional Statement 1]

1. Introduction

The primary focus is to better understand the scenarios used by theoperators to offload services from 3GPP network to WLAN deployed andcontrolled by operators and their partners. Both collocated andnon-collocated scenarios for WLAN/3GPP nodes were considered essential.With better clarity of the intended scenarios it is now possible toconsider solutions for these scenarios. However, full details ofoffloading procedures are considered, it is necessary to get a betterunderstanding of some elements that form the foundation of any goodsolution. In particular, the information necessary for offloading andwhich entity should be considered, the UE or the NW, that is responsiblefor coordinating the exchange of the information. This additionalstatement 1 provides some suggestions on these elements that arecritical to offloading success.

2. Discussion

Additional detailed scenarios for collocated and non-collocatedscenarios should also be considered. These include cases where thecoverage involves one or more overlapping WLAN and 3GPP nodes. In allcases, the scenarios of interest always include coverage of both WLANand 3GPP nodes otherwise offloading would not be possible. The idea ofoffloading isn't new and has been studied under eICIC, HetNet, CA andcurrently under small cell enhancement discussion. But unlike offloadingto small 3GPP nodes, the information exchange between 3GPP node and WLANnode isn't well defined from the RAN perspective. Furthermore, it isunclear what information exchange is possible between 3GPP and WLANnodes, especially if a standardized interface is not available.

2.1. Information Needed for Network Selection

In order to support offloading from 3GPP node to WLAN node, the 3GPPnode must consider many factors that must be evaluated before the properdecision can be made for offloading. Examples of the basis for theoffloading decision include the need to relieve congestion, the need toprovide the UE with higher throughput or the need to satisfy certain QoSrequirements for better user experience. Once the decision is made toattempt to offload the UE, the 3GPP network will need to consider whichnetwork and which node is most suitable for the offloading needs.Therefore, certain key information will need to be evaluated as part ofthe network selection process, otherwise, WLAN offloading won't behandled properly. Specifically, the following list of information isconsidered essential for network selection.

-   -   Access and backhaul load    -   Throughput    -   QoS    -   WLAN node Identification    -   Signal strength    -   Link stability    -   Support for WMM capabilities

One of the main considerations for offloading is the need to relieveRAN/NW congestion. The WLAN access and backhaul load must be consideredbefore deciding whether to offload the UE to WLAN, since there may be aneed to retain the UE within the 3GPP node if the WLAN node is morecongested than the 3GPP node. Even if neither network is not fullyloaded, there may be a need to increase UE throughput to provide abetter user experience and the opportunity to offload the UE to analternate network could satisfy such a requirement. Similar concerns maybe applied to QoS, since some services (e.g., delay tolerant services)may be more suitable for WLAN while other services (e.g., voice) may bemore appropriate for 3GPP node.

One of the advantages of offloading is that not all active services needto be served by one network, which means it is an option to allow the UEto be connected to both networks simultaneously to optimize the QoSrequirements. Such offloading decisions should be carefully consideredsince unnecessary simultaneous connections to both networks will resultin undesired UE power consumption.

It will be necessary for the 3GPP node to identify the target WLAN nodefor offloading. The WLAN node's SSID, or more specifically BSSID, is acandidate for identification It will also be necessary to define theprocess for verifying the authenticity of the WLAN node beforeoffloading.

Signal strength is one piece of information that is clearly needed toevaluate the possibility of offloading to a WLAN node. Just as in thecase for mobility between 3GPP nodes, both the source signal strengthand the target signal strength must be jointly considered.

Closely related to signal strength is the need to evaluate the linkstability of the WLAN node. Link stability is a measure of how long theUE can remain connected to the WLAN node which is mainly dependent onthe variations in signal strength. It may not be necessary for the UE tobe connected to the WLAN node to obtain sufficient link stabilityinformation. And as such, UE's mobility also plays a role in how stablethe connection will be. The number of WLAN nodes deployed in a regionmay also affect link stability at any given location. It is still FFShow we would define link stability and which entity defines thisrequirement.

Whether the WLAN and the UE support WMM. With WMM should also beconsidered it may be possible for the 3GPP node to receive theprioritized category of services supported by the WLAN. In particular,it may be possible to support voice service over WLAN. This couldpotentially offer the 3GPP node more options for offloading and reducingUE power consumption if the UE does not also need to be connected to the3GPP node.

Proposal 1: The set of parameters essential to network selection shouldbe decided.

2.2. Collocated Vs Non-Collocated Scenarios

Once the set of parameters from network selection is decided, whetherthere are any differences in obtaining network related parameters forboth collocated and non-collocated scenarios should also be considered.For the collocated scenario, it may be assumed that much of theinformation exchange between the 3GPP node and WLAN node can be obtainedthrough a proprietary interface since they are both located within thesame node. In particular, information exchange including the access andbackhaul load, management of throughput as well as QoS support can betransparently exchanged within the same node. As part of the extensionof the collocated scenario, it should also be possible to support anexternal WLAN node physically separated from the 3GPP node but connectedto the 3GPP node via a fibre optics link much like Scenario 4 among theCA deployment scenarios. These external WLAN nodes will also havesimilar information exchange capability as the collocated scenariossince the 3GPP node will have direct access to the external WLAN nodewithout delay.

For the non-collocated scenario, it isn't clear if the throughput andaccess/backhaul load can be exchanged since a standardized interface isassumed to be unavailable. One possibility would be to obtain the loadinformation through OAM as part of the network implementation. Thelatency associated with the information exchange should not be criticalas long as the load does not change too quickly. If either of thebackhaul loads is congested, it may be more difficult to exchange theinformation in a timely manner. Another possibility is to obtain theload information through the beacon frame transmitted periodically bythe WLAN node or alternatively from the probe response frame. However,such load information may only reflect the access load and not thebackhaul load.

With respect to radio link parameters, there should be no differencesbetween collocated and non-collocated scenarios so all radio linkparameters are assumed to be available for both scenarios.

Proposal 2: The parameters necessary for network selection should beavailable for both collocated and non-collocated scenarios.

2.3. Radio Link Parameters

As previously suggested, it is assumed that radio link parameters suchas signal strength and link stability of WLAN node are readily availablefor either collocated or non-collocated scenarios. From a differentperspective, radio link parameters such as signal strength areindications of the UE's pathloss from WLAN node. This pathloss isdependent on the location of the UE and whether the location is withincoverage of the WLAN node. Therefore, it is conceivable that the 3GPPnode could determine the UE's pathloss from the WLAN node if the 3GPPnode can readily determine the location of the UE relative to that ofthe WLAN node. For the collocated scenario, since the location of the UEis the same relative to both of the nodes, it may be possible toestimate the pathloss from the WLAN node; however the actualimplementation to determine the pathloss may not be straightforward asthe frequency band and the antenna configuration between the 3GPP andWLAN will differ. The situation is even more complicated with thenon-collocated scenario. The complexity involved in finding relativepathloss of the UE from a non-collocated WLAN node is prohibitive andmay even require the UE to report location information. Also it shouldnot be assumed that the location of the WLAN node is always known by the3GPP node.

To arrive at a common solution for both the collocated and thenon-collocated scenario, it would be much simpler to allow the UE todetermine the radio link parameters and report these to the 3GPP node asneeded. As described above, it is very challenging for the 3GPP node todetermine the UE's WLAN signal strength, and this solution is consistentwith the existing behaviour for mobility among 3GPP nodes, so therewould be little complexity for the UE to add WLAN support for radio linkmeasurements.

Proposal 3: Discuss whether operator WLAN radio link information shouldbe obtained from the UE.

2.4. Offloading Indication

Assuming Proposal 3 is agreeable, the UE could readily obtain the radiolink parameters whenever the UE is within coverage of the WLAN node.This information may be reported to the 3GPP node and the 3GPP nodecould consider whether offloading is needed. However, this assumes theUE's WLAN radio is always on which is not always true. The user or theUE may have turned off the WLAN radio to conserve power. If the UEdoesn't know the 3GPP node's intention for offloading, there may belittle reason for the UE to turn on its WLAN radio. Therefore, it wouldbe beneficial for the 3GPP node to indicate its intention for offloadingto the UE so that the UE may turn on its WLAN radio and measure theradio link parameters in a timely manner. Although this issue is closelytied to the subject of WLAN discovery/scanning optimization, such anindication will be beneficial regardless of which solution is ultimatelyadopted for WLAN discovery/scanning.

Proposal 4: 3GPP network should have a mechanism to inform the UE thatWLAN offloading is needed.

3. Conclusion

This additional statement 1 describes some of the essential elementsneeded for network selection.

[Additional Statement 2]

1. Introduction

As a result of the discussion about how solutions (Solution 1, 2 and 3)can fulfill the requirements, Solution 2 seems to fulfill allrequirements; although there remain a few unclear points, especially asthey relate to ANDSF and RAN rules. This contribution provides furtherexplanation on the differences and how they may be used to meet thetraffic steering requirements. Further details on the fulfilment ofrequirements for Solution 2 are described in the Annex.

2. Discussion

2.1. ANDSF Vs RAN Rules

A few unclear points were described under Solution 2 for fulfillment ofall requirements. Majority of the concerns come from the relationshipbetween ANDSF policy and RAN rules. For example, some concerns come fromthe unpredictability of UE behavior or potential ping-ponging caused byunclear relationship between ANDSF policy and RAN rule. The answers tothe issues below should help to clarify the relationships between ANDSFand RAN rules.

1) If ANDSF is not available, should RAN rules be used?

If ANDSF is not available, RAN should provide rules to ensure consistentbehavior among UEs. Pre-provisioning of UEs with static rules may leadto unpredictable behavior since this is basically up to UEimplementation. This flexibility is one of main advantages with Solution2.

2) If ANDSF is available to the UE, which rule should the UE follow,ANDSF policy, RAN rules or both?

It is currently stated that, “Even if the ANDSF policy is provided tothe UE, RAN has the option to indicate the preferred rule to be used bythe UE”. In principle, the UE should be allowed to use ANDSF if it isavailable to the UE and the UE supports ANDSE However, to prevent anyconfusion, the decision of which rule to use is up to RAN to decide. IfRAN knows that UE has ANDSF available, RAN should allow the UE to useANDSF. If we allow the UE to use ANDSF when RAN has informed the UE thatRAN rules should be used then the use of ANDSF would be left to UEimplementation which would prevent uniform behavior among all UEs.Therefore, either the RAN rules or ANDSF policy would be used as decidedby the RAN and not both.

3) If ANDSF is only available to some UEs but not all UEs (maybe someUEs are not ANDSF capable) could the RAN provide its rules only to thoseUEs without ANDSF?

It will be up to the RAN to decide whether to apply RAN rules or ANDSFpolicy. In our view, RAN rule should be provided to all UEs withoutdistinction to avoid any confusion.

4) Do we apply the same rules for roaming UEs? Will the roaming UEs havethe same ANDSF as the non-roaming UEs? Is it necessary for the roamingUEs to behave the same way as the non-roaming UEs?

Again, it will be up to the RAN to decide whether the UE uses RAN ruleor ANDSF. Roaming UE's behavior can be predictable for operators if theUE performs traffic steering based on the rule provided by RAN. It isalso good for load balancing.

5) Are there any cases where UE implementation is allowed when the UE isinformed by the RAN to use RAN rules?

Following RAN rules does not imply the UE will automatically scan forWLAN and steer traffic to WLAN. RAN rules assume the UE may also accountfor its battery level status as part of WLAN scanning optimization.Details of WLAN scanning optimization is FIN. For traffic steering fromRAN to WLAN, the UE selects traffic to be steered based on the specifiedDRB within RAN rules. For the selection of traffic to be steered fromWLAN to RAN, the UE may use IFOM if available or UE implementation.

Table 1 summarizes the relationship between RAN rules and ANDSF.

TABLE 1 UE's action UE's action RAN's Rule (if ANDSF is (if ANDSF isPreference Available) Unavailable) RAN Rules RAN Rules RAN Rules ANDSFPolicy ANDSF Policy UE uses legacy behavior

Based on the above clarifications, we arrived at the followingconclusions:

For Solution 2, RAN decides whether the UE uses RAN rules or ANDSFpolicy.

Proposal 1: If RAN decides that UE should use RAN rules, the UE willonly use RAN rules even if ANDSF is available.

Proposal 2: If RAN decides that UE should use RAN rules, trafficsteering from RAN to WLAN will be according to the traffic informationwhich defines the data bearer selected for offloading.

Proposal 3: For traffic steering from WLAN to RAN, the UE may selecttraffic according to UE implementation or IFOM (if available).

2.2. Clarification on Load Information

In previous discussions, there were suggestions that RAN may indicateits load to the UE in order to trigger the traffic steering from RAN toWLAN. Such an indication has no benefit for operators. For loadbalancing, Solution 2 allows the RAN to adjust thresholds of 3GPP RANRSRP, RSCP, WLAN BSS load and WLAN RSSI to vary the level of offloadingdesired. Additionally, accuracy of access network selection is alsoimproved by using direct metrics rather than indirect metrics such asload information.

Furthermore, Solution 2 can avoid inefficient scanning, traffic steeringusing offloading indication (refer to FIG. 22). If load level increases,RAN promotes network selection by sending an offload indication to theUE. UE initiates network selection using this indication as a trigger.The use of such an offload indicating will prevent any unnecessaryscanning of WLAN esp. in the likely case when users turn off the UE'sWLAN module to conserve power. The UE will only consider turning on theWLAN module if it receives the offload indication.

Proposal 4: For Solution 2, RAN may send an offload indication to informthe UEs of its intention for offloading from RAN to WLAN.

Proposal 5: Even if UE receive the offload indication from RAN, UE hasthe option to determine whether WLAN scanning is preferable based on UEimplementation, e.g., battery level.

The left side of FIG. 22 indicates the case there is no need to performtraffic steering. The right side of FIG. 22 indicates UE initiatesnetwork selection using the offloading indication.

3. Conclusion

This additional statement 2 provides further explanation especially forthe unclear points, describes refinement of Solution 2 and concludes thesolution fulfils all the requirements.

4. Annex

4.1. Evaluation of Requirement Fulfillment

With the above clarfications of ANDSF and RAN rules, it would be ofinterest to reconsider whether Solution 2 satisfies the requirementfulfillments.

Requirement 1:

Solution 2 achieves the proper balance between RAN load and WLAN loadAPs by utilizing ANDSF or RAN rules. In particular, RAN rules willspecify thresholds for 3GPP/WLAN signals and WLAN load to controltraffic steering without explicitly providing RAN's load information.Even if ANDSF were available to the UE, RAN will decide whether ANDSF orRAN rules will be ultilized to avoid any potential conflict between thetwo.

If ANDSF is unavailable to UEs, even with smart UE implementation, thepolicies used by the UEs may be different, so the outcome of theoffloading may still be uncertain. With RAN rules, UE's behaviour ispredictable which leads to predictable offloading control.

Unlike Solution 1, Solution 2 has the advatange that RAN can control thetiming of applying the rules which should result in more accurateoffloading control. For dynamic load control, RAN has the option toadjust thresholds as needed to enable timely access network selection.

Requirement 2:

User experience may be improved by specifying the rule that reflectsRAN/WLAN signal qualities and WLAN load. The RAN specified theresholdsand takes into account of existing 3GPP measurement reports, RAN stateand the relative load generated by the UE so that both user experienceand network performance may be improved.

Since Solution 2 is a UE-based access network selection solution,UE-specific needs such as steering IP flow rather than just DRB can bemore easily fulfilled with less signaling.

Requirement 3:

For improving utilization of WLAN, improving user experience andreduction of battery consumption are needed. From this perspective,Solution 2 satisfies the requirement by allowing the UE to take intoaccount of its battery level, proximity to WLAN and QoS needs to achievethe desired results.

Randomization may be applied to prevent excessive number of UEs fromconnecting to WLAN simultaneously.

Furthermore, offloading indication from RAN may be used to preventunnecessary WLAN scanning UE initiates this procedure only if theindication is activated.

Requirement 4:

By specifying rules that allows the UE perform WLAN scanning only whencertain RAN conditions are satisfied, battery consumption may bereduced. For instance, by allowing the UE to scan WLAN channel only whenRSRP is less than a certain threshold, UE's power consumption may bereduced.

Requirement 5:

If RAN decides that the UE should use ANDSF, then the traffic steeringmay be based on ANDSF. If ANDSF is unavailable and the RAN decides thatthe UE should use RAN rules, the RAN may decide which traffic would beoptimal for offloading to WLAN.

Requirement 6:

Solution 2 does not affect existing 3GPP and WLAN functionalities, sothere is no impact to legacy systems.

Requirement 7:

Solution 2 follows existing WLAN scanning/connection mechanisms, sothere is no impact to IEEE or WFA.

Requirement 8:

RAN may provide to the UE a white list (or black list) consisting ofWLAN service set identifiers so that WLAN system distinction ispossible. It is also possible to provision per SSID-thresholds.

In addition, Solution 2 may also rely on ANDSF to define WLAN specificsystem for offloading. RAN policy may also make use of existing ANDSFpolicy.

Requirement 9:

The fulfillment of this requirement is accomplished through the use ofdedicated signalling for specific UEs.

Requirement 10:

By utilizing randomization (e.g. UE performs random backoff beforetesting whether the target cell is accessible or not) and providing adedicated assistant information (e.g. threshold) for each UE,ping-ponging may be prevented. It is FFS whether additional mechanismsare needed.

[Additional Statement 3]

Rule Example: if ANDSF is not available (or not preferred by RAN) if RANRSRP < x or offloading indicator == yes if WLAN RSSI > y and WLAN BSSload < z offload from RAN to WLAN else if RAN RSRP > x′ if WLAN RSSI <y′ or WLAN BSS load > z′ offload from WLAN to RAN else forwards thereceived assistance information to the interworking upper layer of theUE Note: Parameters x, x′, y, y′, z, z′ are provided by Network

Splitting between “If RAN RSRP<x or offloading indicator==yes” and “ifWLAN RSSI>y and WLAN BSS load<z”

The motivation is UE can allow to be scanning optimization (includingWLAN client off) if RAN RSRP>x and offloading indicator==no or notsignaled. And UE do RAN RSRP measurement regardless scanningoptimization is applied or not.

The reason two thresholds “If RAN RSRP<x” and “offloadingindicator==yes” having

Even if RAN does not indicate offloading desired, the UE may still wantto scan for WLAN. It's just a way for the RAN to determine how manypotential UEs may not be offloaded (i.e., those UEs with RSRP>x). Thatway the UE may still report WLAN measurements to the eNB, but that theywouldn't be targeted for offloading to WLAN. Sort of like MDT. So thatRAN can refine the adjustment of “x” in the future. This would only beapplicable for dedicated signaling.

The reason “if WLAN RSSI<y′ or WLAN BSS load>z′” then UE should offloadfrom WLAN to RAN

It's dangerous the decision offload from WLAN to RAN is up to UEimplementation or ANDSF. The important thing here is that the RAN rulescan still be applied to determine if the UE should steer traffic fromWLAN to RAN; however, the selection of traffic to be steered from WLANto RAN will be based on UE implementation. (I.e., If UE applying RANrules move to WLAN, RAN rules should also be used during UE. So UEapplying RAN rules should keep its RAN rules until UE receive updatedparameters (after move back to RAN) to prevent unnecessary ping-pong NWselection. Note Rule preference indicator is included in above “updatedparameters”.

The Necessity of Offload Preference Indicator

Listed parameters are provided by dedicated signaling or broadcastsignaling. (More specific, whether all listed parameters are provided bydedicated signaling or there is a possibility that some parameters canbe provided by broadcast signaling.) If there is a situation that RSRPthreshold and WLAN related threshold are provided by broadcast signalwhereas remaining parameters are provided by dedicated signaling, RANshould not change RSRP threshold drastically. Then the Offloadpreference indicator is useful for NW making only UEs located in closeto the WLAN move to WLAN, (if NW knows WLAN and UE's location.)

Of course, there is another possibility that NW send the updatedparameters x, y, z by dedicated signaling instead of Offload preferenceindicator.

To summarize above procedure, UE may obey the rules described in belowtable 2.

TABLE 2 If UE connect to WLAN If UE connect to RAN Assuming RAN RSRP < xN/A if (WLAN RSSI > y and load level isn't Offload WLAN BSS load < z )=> acceptable preference Traffic steering based on indicator == yes RANrule else => RAN RSRP > x N/A if (WLAN RSSI > y and Offload WLAN BSSload < z) => preference Traffic steering based on indicator == yes RANrule else => RAN Assuming RAN RSRP < x N/A if (WLAN RSSI > y and loadlevel is Offload WLAN BSS load < z) => acceptable preference Trafficsteering based on indicator == no RAN rule else => RAN RSRP > x N/A RANOffload preference indicator == no RAN RSRP > x′ if (WLAN RSSI < N/A y′or WLAN BSS load > z′) => Traffic steering based on UE implementationelse => WLAN RAN RSRP < x′ WLAN N/A

[Additional Statement 4]

1. Introduction

One of the primary objectives of this study item is to determine howaccess network selection is handled and how traffic is selected forsteering. With regards to access networks selection, 3 candidatesolutions are currently included in TR37.834. However, it is unclear howthe access networks selection procedure is initiated. It is an issueespecially for UE-based access network selection such as Solution 1 andSolution 2 since the UE behaviour needs to be well defined. Fornetwork-based solution (i.e., Solution 3), access network selection forIDLE UEs may use similar techniques as UE-based solutions; therefore,this is a common issue for all access network selection solutions. Thiscontribution clarifies the issues related access network selection andprovides some recommendations.

2. Discussion

To achieve bi-directional load balancing, access network selection mustbe properly controlled. The procedure for triggering network selectionshould be based at least on the RAN's load condition. And the RAN shouldbe able to provide the most up-to-date load information to the UE.

However, many operators prefer not to provide direct load information tothe UE (i.e., either as a percentage of load or as high/middle/lowindication). Therefore, it may be preferable for the RAN to provideaccess network selection initiation trigger to the UE instead ofproviding direct load information, as illustrated in FIG. 23.

Proposal 1: Access Networks Selection Indicator should be used as atrigger for network selection.

It is ITS whether the indicator is an explicit indicator (e.g., a 1-bitindicator) or an implicit indicator implicitly included as part of theRAN provided parameters (e.g., by adjusting thresholds). Either of thetwo methods should be able achieve the same result. The implicitindicator may be a conditional expression for prompting an offload or anonload. For example, the indicator may be used for adjusting thresholdsso as to prompt an offload or an onload. The indicator may be used forconfiguring offset values so as to prompt an offload or an onload.

2.1. Access Network Selection Indicator

Hereinafter, the discussions are mainly focused on Solution 2. It isassumed that RAN can switch value of the indicator depending on its loadcondition.

For access network selection, RAN should have the flexibility to satisfythe following network selection conditions.

Condition 1: RAN should be able to indicate to all UEs (both IDLE andCONN) to trigger network selection.

Condition 2: RAN may select specific UEs to trigger network selection.

Condition 3: It is not expected that RAN would only select IDLE UEs fornetwork selection.

Both broadcast and dedicated signalling may be used for triggeringnetwork selection. This means RAN may provide both broadcast indicatorand dedicated indicator to the same UE. In general, broadcast indicatoris useful since the coverage size of WLAN is smaller than the macrocell, since it is difficult for the RAN to know which UE is withinproximity of WLAN coverage. Dedicated indicator has the advantage thatthe RAN can configure a specific UE for access network selection (e.g.,based on the UE's resource usage in the RAN). Therefore, the twoindicators do not serve the same purpose and may even be setdifferently. Therefore, RAN2 should consider whether broadcast indicatorand dedicated indicator should be applicable to both IDLE UEs and CONNUEs so that UE's behaviour can be better understood. It should bealready clear that dedicated signalling is applicable for specific UEsso the main question is whether the broadcast indicator should beapplicable to all UEs or just the IDLE UEs. There are 2 candidateoptions.

1) Broadcast network access indication is only applicable to IDLE UEs.

With this option, it would be clear which signalling mechanism isapplicable to which type of UEs. This option would prevent any need toresolve any conflict for UEs receiving both types of indicators.Although this option can satisfy the 3 conditions stated above, it mayresult in excessive signalling. For example, if the RAN wants all UEs totry and select WLAN, RAN will need to broadcast the network selectionindicator and also send dedicated indicators to all CONN UEs.

2) Broadcast network access indication is applicable to all UEs.

With this option, the UE behaviour needs to be well defined since theCONN UEs may receive RAN indicators from either the broadcast signallingor dedicated signalling or both. However, this option does have thebenefit that a single broadcast indicator can satisfy condition 1 above.For condition 2, the RAN may decide not to send broadcast indicator.Instead, RAN may send dedicated signalling to selective UEs (e.g., basedon resource usage) for offloading. This option is useful when the RAN'sload is moderate (e.g., middle) or when RAN's load is increasinggradually. Furthermore, providing the indicator to specific UEs may helpto avoid mass toggling.

Since option ii) may result in the condition that the UE receivedindicators from both broadcast signalling and dedicated signalling, itis necessary to consider the interaction between the two indicators assummarized in Table 1. With option ii) the UE behaviours may becategorized in 3 patterns, UE Behaviour Type 1, 2, and 3 as depicted inTable 3. Table 3 basically suggests that offload indicator via dedicatedsignalling should override offload indicator via broadcasted signalling,since RAN may have specific reason(s) for configuring network selectionfor a specific UE.

TABLE 3 Example of UE Behaviour in connected mode Broadcasted Accessnetwork Broadcasted Broadcasted selection indicator access networkaccess network provided via selection selection broadcast signalling isindicator == indicator == Dedicated signalling not supported ON OFF*Access network selection UE Behaviour Type 1 UE Behaviour UE Behaviourindicator is not provided UE initiate Type 2 Type 3 via dedicatedsignalling selection Conn. UE Conn. UE procedure without initiates doesnot indicator using. selection initiate It is up to UE procedureselection implementation procedure when UE should initiate selectionprocedure. Dedicated access network UE Behaviour Type 2 UE Behaviour UEBehaviour selection indicator == ON Conn. UE initiates Type 2 Type 2selection Conn. UE Conn. UE procedure initiates initiates selectionselection procedure procedure Dedicated access network UE Behaviour Type3 UE Behaviour UE Behaviour selection indicator == OFF Conn. UE doesType 3 Type 3 not initiate Conn. UE Conn. UE selection does not does notprocedure initiate initiate selection selection procedure procedure *Itis FFS whether the RAN will always need to provide a broadcast indicatorset to “OFF” or simply not sent any broadcast indicator when it has nodesire to offload any UE to WLAN.

Proposal 2: Broadcast network access indicator should be applicable toboth IDLE UEs and CONN UEs.

2.2. Scenarios for Access Network Selection

2.2.1. UE is Connected to RAN

If Proposal 2 is agreed, UE will initiate access network selectionaccording to Table 1.

2.2.2. UE is Connected to WLAN (Attached to RAN)

Since the UE cannot receive dedicated indicator, the UE will initiateaccess network selection according to broadcasted indicator only. It isFFS if the UE can still continue the use the dedicated indicator afterit transitions to IDLE and connected to WLAN. Additionally this UE canalso determine whether to reselect back to 3GPP RAN if(measured_metricA>threshold3)∥(measured_metricB<threshold4).

3. Conclusion

This additional statement 4 proposes the benefits of using an accessnetwork selection indicator and describes UE's behaviours when suchindicator is received at the UE. In conclusion, it is beneficial toprovide such indicator from 3GPP RAN to UEs. If broadcast networkselection indicator is applicable to both IDLE UEs and CONN UEs, the UEbehaviour as shown in Table 3 should be clarified.

INDUSTRIAL APPLICABILITY

The present invention is useful for radio communication fields.

The invention claimed is:
 1. A communication control method comprising:controlling a network selection operation to select, from a cellularradio access network (RAN) and a wireless local area network (WLAN), anaccess network with which traffic of a user terminal is exchanged;transmitting dedicated parameters from a first cellular base station tothe user terminal using a unicast radio resource control (RRC)signaling, the first cellular base station being included in thecellular RAN, the user terminal being connected to the first cellularbase station, and the dedicated parameters being used for the networkselection operation to prompt traffic steering between the cellular RANand the WLAN; and after transmitting the dedicated parameters from thefirst cellular base station to the user terminal, transferring the samededicated parameters as the transmitted parameters, from the firstcellular base station to a second cellular base station, in response tothe user terminal performing a handover from the first cellular basestation to the second cellular base station, wherein the transferreddedicated parameters enable the second cellular base station todetermine whether a change of configuration indicated by the transferreddedicated parameters is necessary.
 2. The communication control methodaccording to claim 1, further comprising: receiving the configurationinformation at the second cellular base station; determining whether thechange of configuration indicated by the dedicated parameters includedin the received configuration information is necessary; and notifyingchanged dedicated parameters from the second cellular base station tothe user terminal, in response to determining that the change ofconfiguration is necessary.
 3. The communication control methodaccording to claim 1, wherein the dedicated parameters include acellular signal strength threshold, a WLAN signal strength threshold,and a WLAN load threshold.
 4. A cellular base station comprising: acontroller containing at least one processor and at least one memory,and configured to: control a network selection operation to select, froma cellular radio access network (RAN) and a wireless local area network(WLAN), an access network with which traffic of a user terminal isexchanged; transmit dedicated parameters from the first cellular basestation to the user terminal using a unicast radio resource control(RRC) signaling, the first cellular base station being included in thecellular RAN, the user terminal being connected to the first cellularbase station, and the dedicated parameters being used for the networkselection operation to prompt traffic steering between the cellular RANand the WLAN; and after transmitting the dedicated parameters from thefirst cellular base station to the user terminal, transferring the samededicated parameters as the transmitted parameters, from the firstcellular base station to a second cellular base station, in response tothe user terminal performing a handover from the first cellular basestation to the second cellular base station, wherein the transferreddedicated parameters enable the second cellular base station todetermine whether a change of configuration indicated by the transferreddedicated parameters is necessary.